Mustard now comes in dozens of varieties. Why has ketchup stayed the same?

Many years ago, one mustard dominated the supermarket shelves: French’s. It came in a plastic bottle. People used it on hot dogs and bologna. It was a yellow mustard, made from ground white mustard seed with turmeric and vinegar, which gave it a mild, slightly metallic taste. If you looked hard in the grocery store, you might find something in the specialty-foods section called Grey Poupon, which was Dijon mustard, made from the more pungent brown mustard seed. In the early seventies, Grey Poupon was no more than a hundred-thousand-dollar-a-year business. Few people knew what it was or how it tasted, or had any particular desire for an alternative to French’s or the runner-up, Gulden’s. Then one day the Heublein Company, which owned Grey Poupon, discovered something remarkable: if you gave people a mustard taste test, a significant number had only to try Grey Poupon once to switch from yellow mustard. In the food world that almost never happens; even among the most successful food brands, only about one in a hundred have that kind of conversion rate. Grey Poupon was magic.
Ketchup triggers in equal measure all five of the fundamental tastes one food theorist calls it the Esperanto of cuisine.
Ketchup triggers, in equal measure, all five of the fundamental tastes; one food theorist calls it "the Esperanto of cuisine."Ruven Afanador

So Heublein put Grey Poupon in a bigger glass jar, with an enamelled label and enough of a whiff of Frenchness to make it seem as if it were still being made in Europe (it was made in Hartford, Connecticut, from Canadian mustard seed and white wine). The company ran tasteful print ads in upscale food magazines. They put the mustard in little foil packets and distributed them with airplane meals—which was a brand-new idea at the time. Then they hired the Manhattan ad agency Lowe Marschalk to do something, on a modest budget, for television. The agency came back with an idea: A Rolls-Royce is driving down a country road. There’s a man in the back seat in a suit with a plate of beef on a silver tray. He nods to the chauffeur, who opens the glove compartment. Then comes what is known in the business as the “reveal.” The chauffeur hands back a jar of Grey Poupon. Another Rolls-Royce pulls up alongside. A man leans his head out the window. “Pardon me. Would you have any Grey Poupon?”